1. Technical Field
The present invention relates to a zoom lens, and particularly to a projection zoom lens which is applied to a projection type display device.
The present invention also relates to a projection type display device equipped with such a projection zoom lens.
2. Description of the Related Art
In recent years, accompanying the popularization of personal computers and the like, demand for projection type devices (projectors) is increasing and the market thereof is greatly expanding.
Light valves which optically modulate video signals and image signals to change them into optical signals are used for the projection type display device. A transmissive liquid crystal display element is a known type of light valve. Optical systems, to which the transmissive liquid crystal display elements are applied, generally employ cross dichroic prisms to compose colors. In this case, the reduction side of the projection zoom lens is made telecentric in order to improve the color composition characteristics thereof.
Further, due to increasing demand to obtain higher-definition projection images with high contrast ratios, the projection type display devices, onto which DMD's (Digital Micromirror Device: registered trademark) are mounted as the light valves, are drawing attentions in recent years. In the case that DMD's, which are reflection type light valves, are employed, there is no need for the reduction side of the projection zoom lens to be telecentric. Accordingly, a pupil position can be set near a panel, and thereby a lens part on the reduction side can be miniaturized.
Further, there is demand for the projection zoom lenses to have high zoom ratios and be capable of changing magnification, from the viewpoint of installation properties of the projection type display device.
Conventionally, the projection zoom lenses disclosed in Patent Documents 1 and 2 (Japanese Unexamined Patent Publication No. 2004-077950 and Japanese Unexamined Patent Publication No. 2007-271697) are known as those that can meet the aforementioned demands to some extent.